Generally described, operators of networked servers and computing environments (referred to generally as “network sites”) may communicate with users through a variety of channels. For example, operators of network sites may communicate with users through an operator-provided network, through a third-party network, or through a network of networks (e.g., the Internet). These networks may support various mechanisms to secure and authenticate communications, thereby enabling the network site operator to verify the identity of a user communicating via the channel.
Operators of network sites may also communicate with users through channels that have limited or no support for authenticating user identities. Verifying the identities of users who communicate via these channels may require additional effort, or in some instances it may not be possible to verify the identity of a user of a particular communications channel.